Piezo-electric device



Oct. 4, 1938. wl A. THOMAS 2,131,826

PIEZOELECTRIC DEVCE Filed April 5 1937 2 Sheets-Sheet l EN (Uf/L 7 TE'RNEY Oct. 4,1938. W. A THOMAS 2,31,826

PIEZOELECTRIG DEVICE Filed April 5, 1.937 2 Sheets-Sheet 2 TO HEATER 5s SUPPLY To TERMINAL oN TOP COVER BASE 7 THEPMQSTAT ELECTPODE 2-'\v// WM @J2-WM AND GND4 'am ar/T nNvENToR HEATER Bygj ATT@ F N EY Patented Oct. 4, 1938 UNITED STATES PATENT OFFICE PIEZO-ELECTRIC DEVICE Application April 5,' 1937, Serial No. 134,994

13 Claims.

This invention relates to piezo-electric devices and with particularity to such devices as oscillatory crystals for use in electric control systems and the like.

A principal object of the invention is concerned with an improved manner of supporting a piezo-electric crystal to achieve the desired maximum of oscillatory stability.

Another object is to provide an improved arrangement for maintaining the temperature of a piezo-crystal within predetermined limits.

A further object is to provide a compact and light weight temperature-controlled oscillatory crystal which is particularly well suited for use on air-craft and similar locations where it is likely to be subjected to mechanical shocks and vibrations.

A feature of the invention relates to the means for resiliently clamping a piezo-crystal so that it can execute its normal vibrations without changing its bodily position as a whole within the crystal holder, when subjected to shock or vibration.

Another feature relates to the novel means for resiliently supporting and clamping a piezocrystal around its periphery and so that the major portion of the crystal is spaced accurately from its supporting base and cooperating electrode.

Another feature relates to an improved housing structure for a piezo-crystal whereby the crystal is rendered substantially independent of external ambient temperatures.

A further feature relates to an improved form of anvil or Abase support for a piezo-crystal.

A further feature relates to an improved thermostatic control and heating arrangement for a piezo-crystal whereby maximum uniformity of crystal temperature can be maintained.

A still further feature relates to the novel organization, arrangement and relative location of parts which go to make up a simple and accurate temperture-controlled piezo-electric crystal.

Other features and advantages not specifically enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims.

While the invention will be illustrated as embodied in one particular form, it will be understood that this is done merely for explanatory purposes and not by way of limitation. Accordingly in the drawings,-

Fig. 1 is an elevational view, in partial section and with certain parts broken away, of a piezoelectric control device according to the invention. j

Fig. 2 is a vertical sectional view of the device of Fig. 1 taken along the vertical axis.

Fig. 3 is a horizontal sectional view of Fig. 2 taken along the line 3-3 thereof and viewed in the direction of the arrows.

4 is a horizontal sectional View of Fig. 2 taken along the line 4-4 thereof and viewed in the direction of the arrows.

Figs. 5 and 6 are schematic wiring diagrams showing the various connections to the electrodes and to the heating control circuit.

Fig. 7 is a detailed view of the anvil, heater and thermostatic control members.

Fig. 8 is an enlarged detail view of one of the springs for clamping the crystal.

General description In general the device according to the invention comprises a piezo-crystal of quartz or other suitable piezo-electric substance preferably, although not necessarily, in the form of a flat disc or plate ground to the requisite dimensions in accordance with the frequency or frequencies desired to be controlled. This crystal is supported at a plurality of points around its periphery on a metallic base or anvil which is provided with an integral circular ridge of accurately machined surface and depth. This ridge in conjunction with the crystal provides an accurately dimensioned air chamber or cushion beneath the main body of the crystal. The periphery of the crystal is resiliently clamped at a plurality of points by resilient members such as coiled phosphor-bronze springs each of which is provided with independent tension adjusting means to control the clamping pressure on the crystal. The anvil or base on which the crystal is supported, carries on its interior a thermostat; and a suitable heater controlled by the thermostat surrounds and is supported by the anvil. The anvil forms the base of a bi-part metallic housing, the other part of which is in general of inverted cup-shape formation. The base of this cup-shape member insulatingly carries, in an adjustable manner, an electrode which is arranged to be adjusted to the desired spaced relation with the upper face of the crystal. rI`he entire assembly is enclosed in a bi-part heat insulating housing of nbre, Bakelite or the like, the base of which is removable and provided with a plurality of contact prongs in the manner of a radio tube or the like, the prongs beingelectrically connected internally of the housing to the various elements,

namely the anvil, adjustable electrode, heater, thermostat, etc. Preferably a packing of felt or other heat insulating and vibration deadening material isprovided between the crystal assembly and the inner wall of the insulating housing. In one embodiment, in order to reduce the possibility of stray coupling between certain of the connections there is provided a top cap contact which enables the device to be connected to the grid or other control electrode of a vacuum tube oscillator of the top cap Contact type.

Detailed description Referring more particularly to Figs. 1, 2 and '7, the crystal holder proper comprises a base or anvil designated generally by the numeral I, which is provided with a circular body portion 2 formed at its upper end with an integral iiange 3 having a peripheral bead or edge 4. The upper face of the anvil is undercut to provide an annular ridge 5 upon which the periphery of the piezocrystal Ei rests. Preferably, although not necessarily, the crystal 6 is square or rectangular in shape so that the corner portions rest on ridge 5, the crystal being yieldingly clamped against the ridge 5 by means of a flat annular metal member 1. Member l is provided with openings through which freely pass the adjusting screws 8 which at their lower ends are in threaded engagement with corresponding threaded holes 9 in the flange 3. Interposed between the upper face of member 'I and the heads of screws 8 are corresponding coiled phosphor-bronze springs I El which surround the unthreaded shanks of the screws. Preferably the under face of each screw head is roughened as shown in magnified form in Fig. 8 so that the upper end of the corresponding spring engages this roughened surface and assists in retaining the screw in its adjusted position.

The circular body portion 2 of the anvil is provided with an axially transverse bore Illa in which is mounted a thermostat-controlled contact set described in detail hereinbelow. Attached to the peripheral face of member 2 by means of screws I I is a heater assembly comprising a resistance wire I2 wound around a flat strip I3 of mica or other suitable flexible insulating material. In order to insulate the heater wire from the anvil a layer I4 of mica cloth or similar insulating material underlies the heater assembly. The ends of resistance wire I2 are fastened to appropriate contact terminals or lugs I5 which are fastened to the strip I3 as for example by metal eyelets I6. Preferably the strip I3 is shorter in length than the circumference of the member 2, but nevertheless it should preferably be long enough so that its ends partially overlie the front end of bore I 0 to prevent horizontal dislodgment of the thermostat assembly. Preferably also the screws II are long enough to abut against the block I'I to hold the latter firmly in place.

As shown clearly in Figs. 2 and 7, the thermostat assembly comprises a rigid strip or block I1 of suitable insulation such as Micarta fibre, Bakelite, ceramic or the like. The block I7 is just slightly smaller than the internal diameter of bore Ina so that when positioned therein it is prevented from appreciable vertical dislodgment. Likewise, block I1 is of a length substantially equal to the length of bore I 3a so that when the heater assembly is fastened in place around the anvil 2, it effectively prevents longitudinal dislodgment of the thermostat assembly. The under face of member 2 is cut away as indicated by the numerals I8 and I9 to accommodate the downwardly depending contact lugs or terminals 20, 2l fastened to block Il, for example by metal eyelets 22. If desired, the lugs 20, 2| may be provided with a suitable insulating covering (not shown). Adjustably mounted on the block I'I at one end thereof is a silver pointed contact 23 having a shank threaded through the block. Cooperating with the contact 23 is a spring Contact member 24 which may be fastened to the block by the same eyelet which fastens the lug 2|. Also fastened beneath the spring 24 by eyelet 2| is a bi-metallic strip 25 of material ordinarily employed in electric thermostats. It will be noted that the free end of the bi-metallic strip is curved slightly upwardly to engage the spring 24. This bi-metallic element is preferably so 'designed and located with respect to spring 24 that normally it allows the circuit to be completed through members 23 and 24 to the heater wire, but as the temperature rises above a predetermined point the bi-metallic member ilexes upwardly to open the circuit through the contacts and 24 thus disconnecting the heater from the source of heating current (not shown). With this arrangement, it will be noted that the current flow is not broken directly by the bimetallic element and therefore it is not subject to pitting or sparking, its function being merely to open and close the contacts 23 and 24 mechanically.

fis shown more clearly in Figs. 2 and 3 the cupshaped part of the crystal holder proper comprises a cylindrical metal member 26 adapted to closely around the flange 3 and in engagement with the rim 4. The top 2l of the cup-shaped member is provided with a circular opening 28 and is arranged to be fastened to the flange 3 on anvil I by screws 29. Also fastened to the top 2l by screws 3b is an annular block 3| of a suitable insulation material preferably a ceramic such as Isolantite. Passing through the opening in member Si' is an internally threaded bushing 32, preferably having its lower end split as indicated by the numerals 33, 34, said member 3l having a circular flange through which loosely pass the screws which are in threaded engagement with a correspondingly threaded ring 31. Supported by the bushing 32 is a circular electrode 38 preferably formed integrally with a threaded shank 39 provided with a slot 40 for adjusting the electrode 38 vertically. By the foregoing arrangement the crystal 6 and its cooperating adjustable electrode 38 are substantially completely enclosed in a metallic housing thus effectively shielding the crystal from external electrostatic fields. Preferably the contacting surfaces of the various metal parts of this housing are machined or ground to provide a smooth tight fit between parts, thus completely protecting the crystal from dust or the like. Preferably also the various metal parts of the housing are all of the same light weight alloy such for example as Duralumln. Consequently should the cylindrical part of the housing 26 increase in length with temperature, the shank 39 increases in length to substantially the same extent, thus preventing change of spacing between the crystal and electrode 38 as a resuit of change of temperature. Furthermore, the housing being of good heat conducting metal and being in intimate contact with the anvil, insures uniformity of heat distribution from the anvil to and around the crystal and its associated parts.

The entire assembly as above described comprising the anvil, crystal housing, adjustable u electrode, thermostat and heater are movable as a unit and are positioned within a heat insulating container of moisture-proof heat insulating material such for example as fibre, Micarta, Bakelite or the like. This container comprises an inverted cup-shape portion 4I having tightly tted centrally in the top thereof an internally threaded metal bushing 42 which has fastened thereto at its lower end a double-ended contact spring member 43, adapted to contact with the flange and thus electrically connect with the electrode 38. If desired an additional contact lug 44 may be carried by the member 42 for the purposes to be described. Preferably the inner wall of the housing 4I has cemented or otherwise fastened thereto a layer 45 of heat insulating and vibration dampening material such as, felt, except of course where the member 44 extends through the housing.

In order to hold the crystal and its housing assembly firmly in contact with the member 43 there is provided a sleeve 46 of a suitable heat and electric insulating material such for eX- ample as a paper base Bakelite or the like. Sleeve 46 is provided at its upper end with a rim of reduced thickness so as to engage the flange 3 and the rim 4 accurately as shown in Figs. l and 2. The sleeve 46 is held in abutting contact with flange 3 by means of a base closure member 48 preferably, although not necessarily, of the same material as member 4|, the base being held in place by a series of peripherally spaced screws 49 only one of which is shown in the drawings, and also by a central screw 50 which is adapted to be threaded into the bottom of the anvil as shown in Figs. 1 and 2. The base 48 has fastened therein in any suitable manner, as by riveting, a series of contact prongs 5I, 52, 53. Another contact prong 54 may loosely pass through the base and threadedly engage the anvil. Preferably, although not necessarily, the contact prongs are located the same as those on the usual five-prong radio tube base, so that the device may be plugged into any usual fiveprong radio tube socket.

In some cases where the device is to be used with a. radio tube oscillator of the top-cap contact type, for example the usual screen-grid type of radio tube, it is desirable to reduce the length of the interconnecting wires to the minimum. In these cases, there is threaded into the metal bushing 42 a contact cap 55. In other cases, where this top-cap contact is not required an insulator ferrule may be screwed into the bushing 42 in place of cap 55. In these latter cases a wire (not shown) connects the lug 44 to a small metal insert 56 which is tightly fitted into the lower end of the wall 4I and held in place by a pin or screw 51. A contact screw 58 passes through the base 48 and is threaded into the bottom of the metal member 56.

While the device as above described may be used in any type of control circuit it is usually employed in connection with a grid controlled oscillator tube and the circuit connections for such use are schematically illustrated in Figs. 5 and 6. Fig. 5 shows the manner of connecting the various electrodes and parts externally of the device to the respective contact prongs as viewed from the bottom of the device, and the same numerals are employed to indicate corresponding parts in this ligure as in the preceding figures. It will be noted that in Fig. 5 the connection to the grid of the oscillator tube is made from prong 5I which may be connected by a jumper` t0 screw 58, whereas in Fig. 6 the connection to the grid of the oscillator tube is taken from the top cap 55. If desired an additional contact prong 56 may be provided and connected to the thermostat contact 24 by a wire 51 so that g an external heat cycling indicator or other device may be connected thereto.

While specic materials and proportions of parts have been disclosed herein it will be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention. Thus while the use of a ring has been mentioned herein, it will be understood that it is not limited to a circular ring, but that the clamp member 1 may be square, rectangular, elliptical or other shape so long as it is capable of resiliently clamping the crystal at a plurality of points adjacent the periphery, and so long as it provides an adjustable air chamber between the upper f'ace of the crysi tal and the electrode 38. Likewise while the crystal has been shown as having its lower face spaced from the anvil proper by a circular ridge, any other equivalent manner of accurately spacing the crystal from its'supporting member g may be used. For example a plurality of bosses or projections may be provided on the upper face of the anvil, upon which the corresponding parts of the crystal rest. The important requirement is that the crystal be mounted so that it is provided With an air chamber adjacent its lower face, and with an adjustable air gap between its upper face and the cooperating adjustable electrode. In other words the crystal is clamped around its periphery in the nature of a clamped diaphragm so that apart from the resilient clamping member, its vibrations are damped substantially entirely by the air chamber above and below the crystal. This arrangement permits the resilient clamping force on the periphery of the crystal to be adjusted independently of the adjustment of the gap between the electrode 38 and the crystal face.

What I claim is:

l. A piezo-electric crystal device comprising an enclosing chamber formed of a cylindrical metal member closed at its upper and lower ends, the closure for the lowerI end comprising a disc-like member having a ridge within the chamber to support a crystal thereon in spaced relation to the face of said lower closure member.

2. A device according to claim l in which the lower closure member is provided with an extension carrying a heater assembly and a thermostat, and the upper closure carries an electrode adjustably mounted therein.

3. A piezo-electric crystal device comprising a base, means on said base to support a piezo-crystal in spaced relation to the base, a cup-shaped member forming with said base an enclosing chamber for the crystal, an extension integrally formed on said base and having a recess to receive a thermostat, and a heater coil surrounding and supported by said extension.

4. A device according to claim 3 which is provided with an outer heat-insulating and vibration dampening housing.

5. A shock-proof piezocrystal unit comprising an inner metal enclosing housing for the crystal and within which the crystal is resiliently clamped at a plurality of points around its periphery and an outer housing comprised of heat insulating and vibration dampening material.

6. A unit according to claim 5 in which the outer housing is provided with a base having a plurality of Contact prongs.

7. A device of the character described the combination of a piezocrystal, a supporting base for said crystal, means to space said crystal from said base to provide an air chamber adjacent the lower face of the crystal, means to clamp the crystal resiliently to said base, and an electrode mounted opposite the upper face of the crystal and forming therewith an air gap which is adjustable independently of said clamping means.

8. In a device of the character described, a supporting base, means carried by said base to support a piezocrystal in spaced relation thereto, a clamping ring engaging the upper face of the crystal, said clamping ring exposing the greater part of the upper face of the crystal, and an electrode mounted in spaced .relation toV said ring and providing an adjustable air gap defined by the upper face of the crystal and the face of said electrode.

9. A device according to claim 8 in which the crystal is rectangular, and the clamping ring engages only the corners of the crystal.

10. In combination a piezocrystal, a plurality of ring-like members between which the crystal is resiliently clamped around its periphery, providing an air chamber above and below the crystal, and an adjustable electrode mounted in spaced relation to one face of the crystal and adjustable independently of said clamping means.

11. A piezo-electric crystal holder comprising a metal base member means on said base to support a crystal in spaced relation thereto, a cupshaped member forming with said base an enclosing chamber for said crystal, an electrode adjustably mounted in the top wall of said chamber and insulated therefrom, said electrode being provided with a shank adjustably mounted in the top of the chamber, said cup-shaped member and said shank being of metals having substantially the same coeiiicient of linear expansion whereby expansion of the wall of the chamber is compensated for by expansion of said shank.

12. In combination, a metal anvil, an annular ridge formed on the upper face of said anvil, a piezo-electric crystal seated on said ridge, a metal ring engaging the upper face of the crystal, a plurality of springs pressing against the upper face of said ring, and means to adjust independently the pressure of each spring, each pressure adjusting means including a screw passing loosely through the said ring and adjustably threaded into the anvil.

i3. A piezo-electric crystal holder comprising a metal base member, means on said base to support a crystal in spaced relation thereto, a cupshaped member forming with said base an enclosing chamber for said crystal, an electrode adjustably mounted on the top of the said chamber by means of an integral shank, both the shank and the cylindrical wall of the chamber being of duralumin.

WILLIAM A. THOMAS. 

